GFP expression in HepG2 cells transfected with different transfection reagents. (A-D) Fluorescent and bright-field images of green fluorescent protein expression in HepG2 cells for PLGA-based polyplexes (N/P ratio 6) with control 25 kDa PEI (N/P ratio 5) and lipo2000. (A) naked DNA, (B) PEI, (C) PLGA/PEI, (D) lipo2000. The images were obtained at magnification of 100×. (E) Transfection efficiency of the nanocomplex determined by flow cytometry analysis at different N/P ratio (n = 3). The transfection reagents/DNA complexes were prepared at their optimal condition. (F) Transfection efficiency of the nanocomplex determined by flow cytometry analysis at 2 μg pDNA mixed with different volume of nanocomplex (4 μg/μl). The nanoparticles/DNA complexes were prepared at optimal N/P ratio (n = 3).